This invention is directed toward segmented concrete column or pole for use in structural support.
In the structural support industry, segmented concrete columns are typically used in pier constructions where the columns include small, easily handled segments. The segments are precast with aligned ducts to allow for threading of post-tensioning strands through the column once the segments are placed in the field. Segments are often match-cast (i.e., each consecutive segment is used as a form for the next segment) to ensure a close fit and duct alignment for rapid field assembly. The ends of each column segment typically have formed shear keys to facilitate shear transfer between segments and are bonded together in the field with an appropriate structural epoxy. Once the column is assembled, post-tensioning strands are placed through the ducts and tensioned to a predetermined stress level to satisfy both service and ultimate limit state requirements for the pier.
The segmented column provides economic and aesthetic advantages usually ascribed to any precast concrete system. Because the concrete is cast at the plant rather than in the field, environmental conditions that are crucial to freshly placed concrete may be more closely monitored and controlled. The usual result is higher quality concrete that is more durable over the life of a structure. The precise pieces may be cast earlier in the project schedule and then be assembled in the field more quickly than cast-in-place structures thus reducing construction time. Architectural finishes may also be more expediently applied in the plant providing a wider range of appearances for the completed structure. This type of construction can yield significant cost reductions in construction.
The main structural reasons for pre- or post-tensioning any columns or poles are to increase moment capacity and lateral stiffness thus allowing more slender, attractive geometries and to improve durability by minimizing cracking. With an unbonded post-tensioned (UBPT) system in which the concrete is not bonded to the strands, the column has some fundamentally different behavior than a column that is either pre-tensioned or whose strands are grouted in place after post-tensioning. In contrast to the unbonded strands, bonded reinforcement (either mild steel or strand) experiences stress concentrations at flexural cracks in the concrete. These areas on the reinforcement often yield, allowing the primary mechanism for hysteretic energy dissipation and ductility in the column. When the strands are unbonded, stress is not concentrated locally but distributed uniformly along the full length of the strand.
In columns with bonded reinforcement, energy absorption facilitates redistribution of loads and allows changes in damping characteristics of a structure when seismically loaded. On the other hand, because energy absorption is usually achieved through plastic deformation of primary reinforcements, the structure is typically left with large, permanent deformations and cracks. Conversely, the nonlinear but relatively elastic behavior of columns with unbonded reinforcement results in much less energy being dissipated raising concerns of larger deformations under seismic load and sudden, catastrophic failure. Thus, unbonded columns are typically not used in seismic regions. The advantages of the nonlinear elastic behavior are that residual deformations after removal of the load are minimal and post-tensioning force is not lost. As a result, the structure may remain in service or have reduced repair costs after a major earthquake or impact loading.
While segmented columns with either bonded reinforcement or unbonded reinforcement have solved many problems in the art, many other problems still remain.
One objective of this invention is to provide a segmented support including a yield plate connecting adjacent column segments to one another.
Another objective of this invention is to provide a segmented support including elastic strips connected to an exterior surface of the column and adapted to permit deformation between the column segments and return the column segments to their original orientation.
A further objective of this invention is to provide a segmented support including banding strips embedded into column segments at predetermined connection locations wherein the banding strips are adapted to provide confinement to concrete at high stress locations, and prevent spalling.
These and other objectives will be apparent to those skilled in the art based on the following disclosure.